In pat contests, there used to be a rule that required authors to vote for their own stories, with the thinking being that if everyone does that, it's a level playing field. But people complained that sometimes there are three stories that they preferred, plus as the contests grew we had more authors that weren't participating in the votes at all, so the rule was dropped.
In my opinion, there's certainly nothing wrong with voting for your own story. It's not a dick move, because the authors of the stories you are competing against have the option of doing the same. If they choose not to, that's their choice, and you shouldn't feel constrained by it.
I've voted for my own story in both rounds so far.